Involuntary muscle spasms involving the superficial and deep pelvic floor muscles that typically cause painful entry, limiting or preventing intercourse, tampon insertion or pelvic exams. Women with vaginismus do not always experience "pain" and often report the feeling of their partner or a tampon "hitting a wall". Pain is also a common presentation when partial or complete penetration occurs. It may also present as minor discomfort with tampons, pelvic exams or intercoruse.
See http://www.nhs.uk/conditions/vaginismus/Pages/Introduction.aspx for more information.